I've never really used a phone before and I'm thinking of getting a Samsung Galaxy Ace (I hear Samsung is the best and I want a cheap phone)
I was wondering if you need to use 3G to access all features, like can I just connect it to my home internet and do everything for free other than buying apps?
would things like Skype for calls and Facebook for messages over my home internet cost me anything?
Oh and are they easily to jailbreak?

As long as you have a WiFi connection, you can always use that instead of a data connection (unless of course you were to go out of range). You can turn the data connection off entirely too should you want to. WiFi only ever costs the price of the home connection (what's already being paid) anyway. If you get free calls on Skype (to other Skype users?) then they'll be free, and Failbook™ chat is free anyway. If of course you had a plan which included a data allowance then it would be inclusive.

Rooting (Android variant of jailbreaking) varies by device; xda-developers is perhaps the go-to resource for information on that. The subforum for the Galaxy Ace is here.